(emacs)Minor Modes

Minor Modes
===========
Minor modes are optional features which you can turn on or off. For
example, Auto Fill mode is a minor mode in which SPC breaks lines
between words as you type. All the minor modes are independent of each
other and of the selected major mode. Most minor modes say in the mode
line when they are on; for example, `Fill' in the mode line means that
Auto Fill mode is on.
Append `-mode' to the name of a minor mode to get the name of a
command function that turns the mode on or off. Thus, the command to
enable or disable Auto Fill mode is called `M-x auto-fill-mode'. These
commands are usually invoked with `M-x', but you can bind keys to them
if you wish. With no argument, the function turns the mode on if it was
off and off if it was on. This is known as "toggling". A positive
argument always turns the mode on, and an explicit zero argument or a
negative argument always turns it off.
Enabling or disabling some minor modes applies only to the current
buffer; each buffer is independent of the other buffers. Therefore, you
can enable the mode in particular buffers and disable it in others.
Auto Fill mode allows you to enter filled text without breaking lines
explicitly. Emacs inserts newlines as necessary to prevent lines from
becoming too long. Note:Filling.
Outline minor mode provides the same facilities as the major mode
called Outline mode; but since it is a minor mode instead, you can
combine it with any major mode. Note:Outline Mode.
Overwrite mode causes ordinary printing characters to replace
existing text instead of shoving it over. For example, if the point is
in front of the `B' in `FOOBAR', then in Overwrite mode typing a `G'
changes it to `FOOGAR', instead of making it `FOOGBAR' as usual.
Auto Save mode causes the contents of a buffer to be saved
periodically to reduce the amount you will lose in case of a system
crash. Note:Auto Save.
ISO Accents mode makes the characters ``', `'', `"', `^', `/' and
`~' combined with the following letter, to produce an accented letter
in the ISO Latin-1 character set. Note:European Display.
The following minor modes normally apply to all buffers at once.
Since each is enabled or disabled by the value of a variable, you *can*
set them differently for particular buffers, by explicitly making the
corresponding variables local in those buffers. Note:Locals.
Abbrev mode allows you to define abbreviations that automatically
expand as you type them. For example, `amd' might expand to `abbrev
mode'. Note:Abbrevs, for full information.
Line Number mode enables continuous display in the mode line of the
line number of point. Note:Mode Line.
Scroll Bar mode gives each window a scroll bar (Note:Scroll
Bars.). Menu Bar mode gives each frame a menu bar (Note:Menu
Bars.). Both of these modes are enabled by default when you use the
X Window System.
In Transient Mark mode, every change in the buffer "deactivates" the
mark, so that commands that operate on the region will get an error.
This means you must either set the mark, or explicitly "reactivate" it,
before each command that uses the region. The advantage of Transient
Mark mode is that Emacs can display the region highlighted (currently
only when using X). Note:Setting Mark.